yet的用法,出用在现在完成时中可否如下那样放在句首,为何?yet前后是否要加逗号?

题目

yet的用法,出用在现在完成时中可否如下那样放在句首,为何?yet前后是否要加逗号?
例：The sweat ran down his face and his eyes were glassy from his fever.[Yet] he looked straight ahead and kept running.

答案

可以
在现在完成时的句子中,already常用于肯定句,yet常用于否定句和疑问句,但yet还有其他用法.1.用于否定句中,意思是还、尚、迄今、到那时”.例如 he is not yet here.他还未到.at three o”clock they had not yet decided whether to play basketball or not.三点钟时他们尚未决定是否去打篮球.2.用于疑问句中,意思是已经”.例如 is everything ready yet 一切都准备好了吗?3.与比较级连用,意思是更”.例如 you must work yet harder.你还需更努力地工作.4.与once ,again ,another 连用,意思是再”.例如 he has made yet another mistake.他又犯了一个错误.5.用于肯定句中,意思是仍然、还得”.例如 she is yet a child.她还是个孩子.6.用作并列连词时,意思是然而、可是”.例如 he studied hard yet he failed.他学习努力,可是考试仍未及格.
不必加逗号